VPN Set up question

Hello,

I am running 2003 Enterprise Server with XP clients. I was wondering if
someone might give me a hand setting up a VPN.
Ideally I would like to set up the VPN as a Triple DES IPSec encryption L2TP
connection.
That is only assisible by UserA
when he is accessing the server from usera.dyndns.org
All IP traffice from the remote user gets routed though the VPN no matter if
the traffic is on or off the home network.

On a test base I can set up a PPTP connection to the RAS server. From with
in the LAN.
But I'm not sure how to set the rules to make it only accessible from userA
only when accessed from usera.dyndns.org
I'm also not sure how to make sure all traffice from UserA gets routed
though the RAS server to the outside world (idea here is to encrypt ALL
traffic so that forign networks have NO idea what userA is doing besides
haveing the VPN going).

Last but not least what ports need to be opened on my router/firewall

Thank you,

TC